mem: Stop using SlavePort as a base class.

There are other classes like "ExternalSlave" which still have the word
"Slave" in them, but at least this will make the build quit complaining
about the deprecated SlavePort.

Change-Id: I917c2880574cb77ea37c69dc2727ac5e84b83cd5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51529
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/external_slave.hh

@@ -69,7 +69,7 @@ class ExternalSlave : public SimObject
 {
   public:
     /** Derive from this class to create an external port interface */
-    class ExternalPort : public SlavePort
+    class ExternalPort : public ResponsePort
     {
       protected:
         ExternalSlave &owner;
@@ -77,7 +77,7 @@ class ExternalSlave : public SimObject
       public:
         ExternalPort(const std::string &name_,
             ExternalSlave &owner_) :
-            SlavePort(name_, &owner_), owner(owner_)
+            ResponsePort(name_, &owner_), owner(owner_)
         { }
 
         ~ExternalPort() { }
@@ -90,7 +90,7 @@ class ExternalSlave : public SimObject
 
     /* Handlers are specific to *types* of port not specific port
      * instantiations.  A handler will typically build a bridge to the
-     * external port from gem5 and provide gem5 with a SlavePort that can be
+     * external port from gem5 and provide gem5 with a ResponsePort that can be
      * bound to for each call to Handler::getExternalPort.*/
     class Handler
     {